Research On The Measurement System Of Atmospheric Particulate Matter

This paper designed a set of absorption coefficient measurement system by improving the traditional Jamin interferometer based on the theory of photothermal effect.Compared with other particle absorption coefficient measurement system,this device has the advantages of high precision and good stability.The photothermal interference method maintains the natural state of particulates compared to the filter sampling methods,overcome the defects of membrane sampling technology effectively.This method has high sensitivity,fast response characteristics,work under normal temperature.The effect of scattered light is effectively avoided when measured.The excitation beam and the probe beam of the traditional Jamin interferometer are usually coincident in the design of the structure,and it is easy to introduce the additional phase in the interferometer,which leads to the decrease of the measurement precision.The interaction between the probe beam and the exciting beam of the polarization type Jamin interferometer is carried out by the grazing type structure,which effectively eliminates the influence of thermal noise on the interferometer.In this paper,the theoretical basis is photothermal interference method.The main work is focus on hardware design and signal processing.The main work is as follows:1?Build the absorption coefficient of atmospheric particles measurement system based on photothermal interferometry.The overall optical path of the polarized type Jamin interferometer is designed in detail,and analyzes the working principle of each optical device.The design of the four-frequency module increases the measurement precision of the system.The design of the mechanical structure increases the stability of the system.2?The optical path of the interferometer is modulated by an optical chopper and the experimental results are filtered and amplified using a lock-in amplifier,effectively reduce the impact of noise on the experiment.Derive the relationship between the relative absorption coefficient of the particles and the phase change of the interference signal and the power of the exciting light.The experimental data were analyzed by Matlab software,and got the relative absorption coefficient of the particle samples.